I agree with David Meerman Scott, mobile marketing is becoming more popular. More and more businesses are using it through other apps like Foursquare and Layar or their own apps or text messages.
We are getting to the age where we are attached to our mobile devices by a tight leash. We can do everything right from our phone. Email, banking, schedules and entertainment are just a few things we can do through our phones.
Businesses were thinking right when some decided to offer special promo codes through text messages or their apps. I am guilty of receiving text messages from stores and restaurants. The capability is nice knowing you can receive a free drink or product by showing them the message on your phone. People will then see you doing this and ask how. You tell them you receive special promo messages and then they sign up for them as well. Not only did you just do free promotion for the business, but also gave the business another loyal customer who will in turn do their own free promotion.
With Foursquare and Layar, they use the GPS's through our phones. People can use them to find places to eat, places to stay and entertainment. Just look up what people or your friends said about the places and can make your decision right there. No more long web searches to find a place but right through your phone and GPS.
In the future business can send promotions right to the customer if they are certain distance away from the store. How cool is that! I do not believe this is happening right now, but in a couple of years it will be. I cannot wait for that to happen.